Paste connection plug, burying method, and semiconductor device manufacturing method

ABSTRACT

Form a trench in a major surface of a semiconductor substrate, then bury a paste in the trench. The paste contains solids having a conductive substance and a resin, and solvent for dissolving the resin. The solids content of the paste is not less than 60 vol % and a viscosity ratio thereof is not more than 2.

BACKGROUND OF THE INVENTION

To improve the performance and, particularly, speed of an electroniccircuit system constituted by a plurality of semiconductor chips, it hasbecome increasingly important to reduce the length of theinterconnections between the semiconductor chips to a minimum.

For this purpose, a technique of minimizing the interconnections betweena plurality of semiconductor chips by stacking them has been studiedinstead of the conventional method of mounting a plurality ofsemiconductor chips two-dimensionally on a multilayer board. Such asemiconductor device formed by stacking a plurality of semiconductorchips is called a multichip module.

In addition, with the use of a multichip module of this type, differenttypes of semiconductor chips manufactured by different processes can bestacked on each other into one hybrid semiconductor device.

To manufacture a multichip module, vertically stacked semiconductorchips must be electrically connected. For the realization of suchconnection, the present inventors have already proposed the use ofconnection plugs (chip-through plugs) that extend through verticallystacked semiconductor chips to connect them (Japanese Patent ApplicationNo. 9-305784).

BRIEF SUMMARY OF THE INVENTION

A paste according to the present invention is characterized bycontaining solids having a conductive substance and a resin, and asolvent for dissolving the resin, wherein a solids content is not lessthan 60 vol %.

In the present invention, the solids content indicates the ratio ofsolids (e.g., metals, glass, and resins) in a paste, which are left on asubstrate upon hardening the paste to the total paste (solids+solvent).In the following description, this ratio indicates the volume ratiounless otherwise specified.

In the present invention, the solids content of a paste is set to 60 vol% or more for the following reason. When a paste is hardened (dried)after it is buried in a trench with a squeegee, the solvent in the pastevolatilizes.

Upon this volatilization of the solvent, the volume of the pastereduces. If the volume reduction of the paste is large, the trenchcannot be filled with the paste. A deterioration in buried shape due tosuch a volume reduction can be effectively prevented by increasing thesolids content of the paste.

When the solids content is set to 60 vol % or more as in the presentinvention, in particular, occurrence of a volume reduction that causesconnection failures and the like can be effectively prevented, and thetrench can be filled with the paste with a good buried shape.

In addition, another paste according to the present invention ischaracterized by containing solids having a conductive substance and aresin, and a solvent for dissolving the resin, wherein a viscosity ratiois not more than 2.

In the present invention, the viscosity ratio of a paste indicates theratio of viscosity changes in a case wherein the viscosity of the pasteis measured with a rotational viscometer at rotational speeds thatdiffer by one order of magnitude.

Assume that the viscosity of a given paste is measured with therotational viscometer at different rotational speeds, and viscosities of200 Pa·s and 100 Pa·s are respectively measured at 10 rpm and 100 rpm.In this case, the viscosity ratio is 200 Pa·s/100 Pa·s=2. The buryingratio of a viahole is the ratio of the paste to the sectional area ofthe viahole when the cross-section of the viahole is observed after apaste burial test.

In the present invention, the viscosity ratio of a paste is set to 2 orless for the following reason. When the viscosity ratio is high, theviscosity of the paste receiving force from the squeegee becomes low.When the paste receives no force, the viscosity increases. For thisreason, when the paste is buried in a trench with the squeegee, theviscosity of the paste becomes high at the bottom portion of the trench.This makes it difficult to bury the paste.

If, however, the viscosity ratio is set to 2 or less as in the presentinvention, an increase in the viscosity of the paste at the bottomportion of the trench can be effectively suppressed. This preventsformation of voids that cause a connection failure and an increase inresistance. Hence, the trench can be filled with the paste.

Furthermore, still another paste according to the present invention ischaracterized by containing solids having a conductive substance and aresin, and a solvent for dissolving the resin, wherein a solids contentis not less than 60 vol % and a viscosity ratio is not more than 2.

The trench can be filled with this paste with a good buried shape.

In consideration of the buried shape, the viscosity of the above pasteis preferably 200 pas or less. In addition, if the paste is to be usedfor a connection plug, the main component of the paste should be aconductive substance.

A connection plug according to the present invention is a connectionplug made of a paste containing powder particles having differentaverage sizes and buried in a connection hole. This connection plug ischaracterized in that the paste contains 10% or more of a powder havingan average particle size of 3 μm or more.

In this case, the paste preferably contains 10% or more of a powderhaving an average particle size of 1 μm or more. The powder may be themain component of the paste or another component. For example, theconnection hole is a through hole extending through a semiconductorchip.

The viscosity of the paste is determined by the total surface area ofpowder particles in the resin contained in the paste. As the totalsurface area increases, the viscosity decreases. With the use of aconnection plug containing a powder of a large average particle size asin the present invention, therefore, the paste as the connection plugcan be buried in a trench with a good buried shape. In addition,according to the study conducted by the present inventors, it was foundthat the occurrence rate of cracks could be reduced sufficiently bysetting the content of such a powder to 10% or more.

A burying method according to the present invention is characterized inthat a paste according to the present invention is buried in a trenchformed in the surface of a substrate.

With this arrangement, a good buried shape can be realized even by aburying method using a squeegee.

In addition, the burying method according to the present invention ischaracterized in that a powder dispersion is applied on a regionincluding a trench formed in the surface of a substrate, and the powderis precipitated in the solution, thereby filling the trench with thepowder.

According to this arrangement, since the trench is filled with thesmall-volume powder that precipitates, a deterioration in buried shape,e.g., formation of a void, is suppressed.

In this case, as the above dispersion, a solution to which a resin isadded is preferably used. With the use of such a solution, the powderparticles can be temporarily fixed with the resin.

In addition, the powder preferably partially contains glass. With theuse of this powder, the glass melts in a calcination process to fill thetrench without any recess.

A method of manufacturing a semiconductor device according to thepresent invention is characterized by comprising the steps of forming atrench in a surface of a substrate, filling the trench with acalcination type paste formed inside and outside the trench, temporarilyhardening the paste, removing an excess portion of the paste outside thetrench, and calcining the paste.

In the present invention, the excess portion of the paste is removed inthe step of temporarily hardening the paste, in which the paste can beeasily removed, instead of the step after calcination in which the pasteis difficult to remove. Even if, therefore, the width of the trenchincreases, and the amount of paste increases, an excess paste portioncan be removed without taking much time.

According to the present invention, therefore, even if the width of thetrench is increased to decrease the resistance of the connection plug,an increase in the formation time of a connection plug made of a pastecan be suppressed.

Preferred aspects or more detailed forms of the semiconductor devicemanufacturing method according to the present invention will bedescribed below.

(1) The excess portion of the paste outside the trench is removed bypolishing or etching. The above polishing is preferably CMP (ChemicalMechanical Polishing). The above etching is RIE (Reactive Ion Etching)or CDE (Chemical Dry Etching).

(2) After the paste is calcined, the lower surface of the substrate isremoved until the paste appears, thereby forming a connection plug madeof the paste penetrating the substrate. More specifically, the lowersurface is removed by polishing or etching. The above polishing ispreferably CMP. The above etching is RIE or CDE.

In cases (1) and (2), after the trench is filled with the paste to acertain degree, different pressures are applied to portions inside andoutside the trench, thereby filing an unfilled region in the trench withthe paste. Even if the depth of the trench increases, the overall trenchcan be filled with the paste. In these cases, therefore, even if thedepth of the trench is increased to decrease the resistance of aconnection plug, a connection plug made of a paste without any void canbe formed.

(3) After the step of calcining the paste, an interconnection is formedon the paste.

(4) This method is characterized by using a conductive paste (plug body)as the above paste.

In cases (3) and (4), an insulating film is formed in advance betweenthe surface of the trench and the conductive paste. If, however, aninsulating substrate such as a ceramic substrate is used as the abovesubstrate, such an insulating film is not required. Furthermore, if aninsulating paste is used as the above paste, a conductive film(connection plug body) is formed in advance on the surface of thetrench.

In addition, another semiconductor device manufacturing method accordingto the present invention is characterized by comprising the steps offorming a trench in a major surface of a substrate, burying acalcination type paste in the trench so as to fill a space including atleast a portion on a bottom surface of the trench, filling an unfilledregion in the trench with the paste by making a pressure on the pasteoutside the trench higher than a pressure on the unfilled region in thetrench filled with the paste, and removing an excess portion of thepaste outside the trench.

Furthermore, still another semiconductor device manufacturing methodaccording to the present invention is characterized by comprising thesteps forming a trench in a major surface of a substrate, burying acalcination type paste in the trench so as to leave a space including atleast a portion of a bottom surface of the trench, filling an unfilledregion in the trench with the paste by making a pressure on the pasteoutside the trench higher than a pressure on the unfilled region in thetrench filled with the paste, temporarily hardening the paste, removingan excess portion of the paste outside the trench, and calcining thepaste.

According to the present invention, even if the width and depth of atrench are increased to sufficiently decrease the resistance of aconnection plug, an increase in the formation time of a connection plugmade of a paste can be suppressed, and a connection plug made of a pastewithout any void can be formed.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIG. 1 is a graph showing the relationship between the viscosity ratioof a paste and the burying ratio of a viahole;

FIG. 2 is a graph showing the relationship between the solids content ofa paste and the burying ratio;

FIG. 3 is a graph showing the relationship between the average particlesize of large powder particles, the occurrence rate of cracks in thepaste, and the content of large powder particles;

FIGS. 4A to 4F are sectional views showing the steps in a method offorming a chip-through plug according to the second embodiment of thepresent invention;

FIGS. 5A and 5B are sectional views for explaining problems posed in aconventional method of burying a paste in a trench (screen printing);

FIGS. 6A to 6E are sectional views showing the steps in a method offorming a connection plug according to the fifth embodiment of thepresent invention;

FIGS. 7A to 7G are sectional views showing the steps in a method offorming a connection plug according to the sixth embodiment of thepresent invention; and

FIGS. 8A to 8D are sectional views showing the steps in a method offorming a connection plug according to the seventh embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described below withreference to the accompanying drawings.

The present inventors examined the conventional method of forming achip-through plug (Japanese Patent Application No. 9-305784) and foundthe following problem.

When the above chip-through plug is to be formed, a conductive paste asa chip-through plug is buried in a trench (opening diameter: 50 to 100μm; depth: 100 to 150 μm) formed in the surface of an Si substrate. Thelower surface of the Si substrate is then polished until the pasteappears.

As a method of burying the paste, a burying method (screen printing)using a squeegee is used because of its simplicity and easiness.

In the method using the squeegee, however, the trench formed in thesurface of a substrate 81 cannot be sufficiently filled with a paste 82.As a result, a recess 83 or a void 84 is formed.

Such a deterioration in the buried shape of the paste 82 causes aconnection failure or an increase in resistance. This problem becomenoticeable not only when the width of the trench is increased tosufficiently decrease the resistance of the chip-through plug but alsowhen the depth of the trench is increased.

Embodiments of the present invention which can prevent the abovedeterioration in buried shape will be described below.

(First Embodiment)

In this embodiment, a paste is buried in a trench formed in the surfaceof a substrate by a printing method using a squeegee. In theconventional method, as shown in FIGS. 5A and 5B, voids and recesseswere formed in trenches because a paste is not sufficiently buried inthe trenches.

The present inventors found that the causes of this problem were achange in the viscosity of the paste when buried with the squeegee andthe shrinkage of the paste upon volatilization (to be referred to ashardening hereinafter) of the solvent of the paste. To improve theburied shape of a paste, this embodiment therefore uses a paste forwhich a viscosity change upon burial and a solids content arecontrolled.

FIG. 1 shows the relationship between the viscosity ratio of a paste andthe burying ratio of a viahole. In this case, the viahole has a depth of50 to 200 μm and an opening diameter of 100 μm. The paste was buriedunder the condition that the viscosity measured by a rotationalviscometer became 150 Pa·s when the rotational speed was 200 rpm. Theaverage diameter of the paste was set to 1 μm. The viscosity ratio wascontrolled with the resin component of the paste, and the solids contentwas set to 60 vol %.

As shown in FIG. 1, when the viscosity ratio is 3, the viahole having anaspect ratio of 0.5 (depth of 50 μm) exhibits a burying ratio of 90%,but the viahole having an aspect ratio of 2 (depth of 200 μm) exhibits aburying ratio of 40%.

It was found that viscosity ratios of 3 or less, 2 or less, and 1.5 orless needed to be respectively set for the viaholes having aspect ratiosof 0.5 (depth of 50 μm), 1 (depth of 50 μm), and 2 (depth of 200 μm) toensure a burying ratio of 90% or more.

Although the relationship between the burying ratio and the viscosityratio was obtained with the opening ratio ranging from 40 to 200 μm andthe depth ranging from 20 to 400 μm, it was found from the researchconducted by the present inventors that when the viscosity ratio wasconstant, the burying ratio was determined by only the aspect ratioregardless of the depth.

The mechanism of increasing the burying ratio by keeping the viscosityratio constant can be explained by the load imposed by the squeegee inburying the paste. When the viscosity ratio of the paste is high, theviscosity of the paste decreases in the presence of a force from thesqueegee, but increases in the absence of a force. For this reason, theviscosity becomes high at a bottom portion of a trench at which the loadfrom the squeegee is light, hindering the paste from being buried.

As is obvious from the above description, the burying ratio can beeffectively increased by decreasing the viscosity ratio, and a buryingratio of 90% or more can be obtained even at an aspect ratio of 1 bysetting the viscosity ratio to 2 or less.

FIG. 2 shows the relationship between the solids content of the pasteand the burying ratio. In this case, the paste was buried in a trench bydirectly scanning the squeegee on the substrate without using any mask.The viscosity ratio of the paste was 1.5. The paste was buried under thecondition that the viscosity measured by the rotational viscometerbecame 150 Pa·s when the rotational speed was 20 rpm.

As shown in FIG. 2, as the solids content increases, the burying ratioincreases. When the aspect ratio is 1, a burying ratio of 90% or morecan be obtained with a solids content of 60 vol % or more, and a buryingratio of 95% or more can be obtained with a solids content of 70 vol %or more.

As is obvious from FIG. 2, when the aspect ratio is 0.5 or more, aburying ratio of 90% or more can be obtained with a solids content of65% or more, and a burying ratio of 100% or more can be obtained with asolids content of 80% or more.

The relationship between the solids content of the paste and the buryingratio can be explained as follows. When the paste is hardened after itis buried in a trench with the squeegee, the solvent in the pastevolatilizes. As a result, the volume of the paste reduces by the amountof volatilized solvent. If this volume reduction is large, the trenchcannot be filled with the paste, resulting in a great decrease inburying ratio.

As is obvious from the above description, the burying ratio can beeffectively increased by increasing the solids content, and a buryingratio of 90% or more can be obtained even at an aspect ratio of 1 bysetting the solids content to 60 vol % or more.

As described above, the burying ratio can be effectively increased bydecreasing the viscosity ratio (preferably to 2 or less) or increasingthe solids content (preferably to 60 vol % or more). More preferably,the viscosity ratio is decreased and the solids content is increased atthe same time.

In this embodiment, the viscosity of the paste was 150 Pa·s. However, ahigh burying ratio could be realized between 100 to 200 Pa·s as in theembodiment.

To increase the solids content of the paste without increasing theviscosity of the paste to a high value, i.e., a value exceeding 200Pa·s, the density of the solids may be decreased. For example, theamount of resin in the paste may be increased, the glass component maybe increased in amount, or a low-density light metal may be used as ametal material.

Alternatively, the average particle size of the powder in the paste maybe increased. As the average particle size of the powder increases, thesurface area of the powder per unit volume increases. As the surfacearea per unit volume increases, the viscosity increases under theinfluence of the surface tension. This increases the solids contentwhile maintaining the viscosity. Note that the powder may be the maincomponent of the paste or another component.

Although different values were obtained in the paste viscosity range of50 to 400 Pa·s, similar tendencies were found in this range. When, forexample, the viscosity of the paste was 200 to 400 Pa·s, and the solidscontent was 60 vol %, the viscosity ratio needed to be 1.5 or less torealize a burying ratio of 90% in a trench having an aspect ratio of 1.This viscosity ratio was lower than that in the embodiment (viscosity of150 Pa·s). Furthermore, a burying ratio of 90% or more could be realizedat a viscosity ratio of 3 or less.

In addition, a high burying ratio can be realized even by using a metal,a glass material, a mixture, or a composite material as a pastematerial.

In this case, to decrease the viscosity of the paste, the particle sizeof the paste is preferably increased or the particle size distributionof the paste is preferably made broad. The particle size distribution ofthe paste may be made broad by using a method of mixing powder particleswith different average sizes. When the particle size distribution ismade broad, the viscosity decreases to improve the buried shape andsuppress occurrence of cracks upon hardening.

When, for example, powder particles having average sizes of 1 μm and 5μm are mixed in an Ni paste, the occurrence rate of cracks in the pastebecomes ½ or less that in an Ni paste obtained by mixing only a powderhaving an average particle size of 1 μm. Note that the powder may bemade of Ni or another material.

FIG. 3 shows the relationship between the average size of large powderparticles, the occurrence rate of cracks in the paste, and the contentof large powder particles (large powder particles/all powder particles[wt %]) when powder particles containing large powder particles having asize of 1 μm or more are mixed in the paste. In this case, the averageparticle size of the paste is 1 μm, and the average sizes of the largepowder particles are 1 μm, 2 μm, and 3 μm, respectively.

As is obvious from FIG. 3, when the large powder particles having anaverage size of 3 μm are used, the occurrence rate of cracks in thepaste can be suppressed to 80% by setting the content of the largepowder particles to 10% or more, and the occurrence rate of cracks canbe suppressed to about 20% or less by setting the content to 60% ormore.

In practicing the present invention, in consideration of its mechanism,the resin and solvent in the paste need not be specified. Even if, forexample, ethyl cellulose, terpineol, or acrylic resin is used as aresin, the paste can be buried in the same manner as in this embodimentas long as the above conditions for viscosity ratios and solids contentsare satisfied.

When a metal paste is used, the amount of resin is preferably small inconsideration of a decrease in resistance. When a paste was to befinally formed in only a trench, in particular, only a minimum amount ofresin was required for temporary holding, and 3% or more of the totalpaste was sufficient for the amount of resin for temporary holding.

In addition, if the amount of resin is 6 wt % or more, since the solventand solids in the paste do not separate from each other, long-termstorage is facilitated. If, therefore, a paste is to be simply formed,the amount of resin is preferably 6 wt % or more.

If the wettability between a paste and a substrate was poor in a buryingprocess, the buried shape deteriorated. When the viscosity of the pastewas 50 Pa·s or less, in particular, the buried shape was improved byimproving the wettability between the paste and the substrate. Forexample, the wettability can be improved by performing ultrasoniccleaning of the substrate with the solvent in the paste, cleaning thesubstrate with a surfactant, or using a surfactant-containing paste.

(Second Embodiment)

In this embodiment, a chip-through plug (connection plug) for amultichip module is formed by using a paste having excellent buryingcharacteristics as in the first embodiment.

The following conditions are required for a chip-through plug. Thechip-through plug must be sufficiently buried in a trench to allow thechip to make lower-surface contact. The upper portion of thechip-through plug (to be referred to as the plug upper portionhereinafter) must be flat to allow an interconnection to be formed onthe plug upper portion. The lower portion of the chip-through plug (tobe referred to as the plug lower portion hereafter) must havewettability with respect to a repairable material such as a solder andbe dense not to absorb a solder or the like.

As a method of satisfying such requirements, a method of improving theburied shape, planarization, and denseness of a chip-through plug byforming sputtered films on both the plug upper portion and the pluglower portion is available. In this embodiment, however, a method ofimproving these properties by a paste itself. According to this method,a chip-through plug can be formed by using only a paste. Since the stepof forming sputtered films is not required, the process is simplified.

FIGS. 4A to 4F are sectional views showing the steps in a method offorming a chip-through plug according to this embodiment. First of all,as shown in FIG. 4A, a trench is formed in the upper surface of an Sisubstrate 1, and a paste containing materials such as Ni, Cu, and Auexhibiting good wettability with respect to a solder and having a smallparticle size distribution (to be referred to as a fine pastehereinafter) 2 is deposited on the entire surface of the trench to coverthe bottom and side surfaces of the trench. At this time, the trench isnot filled with the fine paste 2.

As shown in FIG. 4B, the trench is filled with a paste having a largeparticle size distribution and exhibiting a high burying ratio (to bereferred to as a buried paste hereinafter) 3 like the one described inthe first embodiment by a burying method using a squeegee.

As shown in FIG. 4C, that excess portion of the buried paste 3 outsidethe trench and the buried paste 3 slightly below the opening surface ofthe trench are removed by polishing or etching. As a result, an unfilledportion is formed in the upper portion of the trench. Thereafter, thefine paste 2 and the buried paste 3 are calcined.

As shown in FIG. 4D, a fine paste 4 is deposited on the entire surfaceof the resultant structure to fill the unfilled portion.

As shown in FIG. 4E, the excess portion of the fine paste 4 outside thetrench is removed by CMP to planarize the upper surface, and the finepaste 4 is calcined. Note that the fine paste 2 and the buried paste 3may not be calcined in the step in FIG. 4C, but all the paste 2 to paste4 may be calcined altogether in the step in FIG. 4E.

Finally, as shown in FIG. 4F, the lower surface of the Si substrate 1 ispolished to expose the fine paste 4, thus completing the chip having thechip-through plug made up of the fine paste 2, the buried paste 3, andthe fine paste 4 and extending through the Si substrate 1.

Note that the use of an appropriate slurry in the step in FIG. 4C willobviate the necessity of the fine paste 4 for planarizing the plug upperportion. More specifically, this step may use a slurry that can removethe main component of a paste (for example, Ni if an Ni paste is used)by CMP in which the contribution of chemical polishing is larger thanthat of mechanical polishing.

The use of such a slurry can prevent the paste 3 and paste 4 from beingphysically polished to an excessively low level by mechanical polishingeven if the upper portions of the paste 3 and paste 4 contain largeparticles of the main components. Therefore, the upper surface can beplanarized.

(Third Embodiment)

As a method of burying a filling member having conductivity such as achip-through plug in a trench, a method of dispersing a conductivepowder with a solvent in advance, applying this powder (powder+solvent)on the substrate in which the trench is formed, and precipitating thepowder in the solvent, thereby burying the powder in the trench isavailable in addition to the method of burying a paste with a squeegee.

For example, an Ni powder having an average particle size of 1 μm isdispersed in a methanol solution, and the solution is applied to asubstrate in which a plug is formed. Since the dispersed NI powderprecipitates, the Ni powder is deposited on the substrate. The substrateis then dried to evaporate the methanol. Thereafter, the Ni powder iscalcined. As a consequence, the powder is completely buried in thetrench (this method will be referred to as the precipitation methodhereinafter). After this process, the Ni powder portion calcined outsidethe trench is removed, as needed.

In burying the powder in the trench by the precipitation method, sincethe binding force between the particles of the powder in the trench islost upon volatilization of the solvent, a resin is preferably dissolvedin the solvent to allow the powder particles to precipitate and combinewith each other upon precipitation of the powder or volatilization ofthe solvent.

As methods of fixing the powder, a method of sealing the powder with aresin upon volatilization of the solvent and a method of forming a filmon the opening surface of the trench are available. In the lattermethod, since no resin is contained in the powder, the powder can becalcined without being influenced by the atmosphere in calcination.

Although the method of fixing the powder has been described above, if novibration is applied to the stage, the powder need not be fixed.

In addition, a chip-through plug for the multichip module of the secondembodiment can also be formed by using the precipitation method of thisembodiment.

More specifically, a powder of a small particle size (fine powder) isprecipitated first, and then a powder of a large particle size (buriedpowder) is precipitated. The buried powder outside the trench and theburied powder and fine powder slightly below the opening surface of thetrench are removed. Finally, a fine powder precipitates on an unfilledportion of the trench. These powder portions may be calcinedcollectively or separately.

Alternatively, the precipitation method may be performed by using apowder obtained by mixing large powder particles and small powderparticles. In this case, the stepped portion on the upper portion can beimproved by performing control such that the large powder particlesprecipitate first, and the small powder particles are deposited thereon.

In the precipitation method described above, wettability between thesubstrate and the solvent used for the method is important. If a solventof poor wettability must be used as a dispersant for the powder, amethod of physically improving the quality of the powder by usingultrasonic waves or a method of improving the quality of the solvent byusing a surfactant must be used together. When, however, the viscositywas about 20 to 50 Pa·s, i.e., the viscosity was relatively high,wettability did not have much influence.

In addition, to shorten the precipitation time of the powder, acoagulant that weakens the effect of the dispersant may be added orprecipitation may be speeded up by using centrifugal force.

(Fourth Embodiment)

In the burying method of a paste using a squeegee (screen printing), theparticle size of the paste, particle size distribution, and particleshape influence paste burial.

The particles of a paste used for a chip-through plug are preferablyfine particles in order to planarize the plug upper portion.

When a paste is to be buried by screen printing, the average size of theparticles of the paste is preferably 0.5 μm or more and 5 μm or less. Inaddition, particles having an average size of 1 μm or less arepreferably 10% or more, and particles having an average size of 3 μm ormore are preferably 10% or more.

When particles having an average size of 1 μm are to be exposed on theplug upper portion, the above particles must be removed by CMP. Theparticles serve as the main component of the paste and other components.

As a particle shape, a shape with a large particle area, e.g., aconfetto-like shape, is effective in increasing the viscosity. Inaddition, owing to many projections of this shape, conduction improvesin calcination, resulting in a decrease in resistance.

The particle size distribution in screen printing is important. If largeparticles are required to control the particle size distribution, theuse of a glass material as such material, which dissolves incalcination, can improve the buried shape and planarization.

If the main component of a paste is Au, it is difficult to increase thesolids content by using only Au because of high density. For thisreason, coating particles containing Ni as a nucleus with Au can improvethe buried shape while taking advantage of the characteristics of thehigh-density material. In addition, if no specific problem arises in aburying process, the buried shape can be improved by intentionallyadding a low-density material.

The present inventors examined the conventional chip-through plugforming method (Japanese Patent Application No. 9-305784) and furtherfound the following problems.

As a method of burying the above conductive paste, a burying methodusing a squeegee (screen printing) is used because of its simplicity andeasiness.

In the burying method using a mask and a squeegee, a conductive pasteportion remains on an Si substrate by the amount corresponding to thethickness of the mask, although it depends on the method to be used.

In a case of a connection plug connected to a power supply line, inparticular, as the width of a trench increases because of requirementsfor a decrease in the resistance of the connection plug, a thickerconductive paste must be applied on an Si substrate. As a consequence, athicker paste portion remains on the substrate.

In the method of burying a conductive paste by directly applying it onan Si substrate with a squeegee without using any mask, an excessconductive paste portion protruding from the squeegee remains on the Sisubstrate.

When the excess conductive paste portion is removed after the conductivepaste is calcined, the thickness of the excess conductive paste portionbecomes as large as several tens μm in either of the above methods.

It takes much time to remove such a thick excess conductive pasteportion by CMP, resulting in an increase in the time required to form aconnection plug. This decreases the productivity of multichip modules.

To further decrease the resistance of a connection plug, both the widthand depth of a trench are increased. In the burying method using thesqueegee, as a trench becomes thicker (aspect ratio increases), thetrench cannot be sufficiently filled with a paste. As a result, achip-through plug having a void is formed.

An embodiment of the present invention which can solve the aboveproblems that arise when the size (width and depth) of a trench isincreased will be described below.

(Fifth Embodiment)

FIGS. 6A to 6E are sectional views showing the steps in a method offorming a chip-through plug according to the fifth embodiment of thepresent invention. In this embodiment, a chip-through plug is formed ina ceramic substrate.

First of all, as shown in FIG. 6A, a trench 12 having, for example, anopening diameter of 100 μm and a depth of 200 μm is formed in thesurface of a ceramic substrate 11 having, for example, a width of 4 cmand a thickness of 0.8 mm. Thereafter, the ceramic substrate 11 iscalcined.

As shown in FIG. 6B, a calcined conductive paste 13 having a thicknesslarger than the depth of the trench 12 is buried in the trench 12 by theburying method (screen printing) using the squeegee and a metal maskhaving an opening portion equal to or larger than the opening diameterof the trench 12, e.g., a metal mask having an opening diameter of 120μm and a thickness of 30 μm. At this time, the excess portion of theconductive paste 13 which protrudes from the squeegee remains on thesubstrate (on the trench 12 and its peripheral portion). The conductivepaste 13 having a thickness smaller than the depth of the trench 12 maybe buried in the trench 12 as long as the trench 12 can be entirelyfilled with the paste finally.

After the conductive paste 13 is temporarily hardened by a heattreatment at 140° C. for 10 min, the excess portion of the conductivepaste 13 outside the trench 12 is removed by CMP or mechanical polishing(MP) using a grindstone, as shown in FIG. 6C.

At this time, since the conductive paste 13 is only temporarilyhardened, the excess portion of the conductive paste 13 outside thetrench 12 can be removed by polishing with a weak force enough todestroy the resin in the conductive paste 13.

As a result, the excess portion of the conductive paste 13 can beremoved at a rate as high as 20 to 100 μm/min as compared with a lowrate of 1 μm/min in the conventional method. In this embodiment,therefore, the excess portion of the conductive paste 13 can be removedin a very short period of time as compared with the prior art.

The conductive paste 13 is then calcined at 500° C. to remove the resincomponent in the conductive paste 13 and ensure conductivity of theconductive paste 13. The conductive paste 13 in this step will bereferred to as the chip-through plug 13 hereinafter.

Finally, as shown in FIG. 7D, the lower surface of the ceramic substrate11 is polished until the chip-through plug 13 appears, therebycompleting the chip-through plug 13 extending through the ceramicsubstrate 11. The above polishing is, for example, CMP or MP. Inaddition, the lower surface may be removed by etching such as RIE or CDEinstead of polishing.

The subsequent steps are the same as those for a general multichipmodule. For example, as shown in FIG. 6E, the subsequent steps are thestep of forming an interconnection 14 connected to the chip-through plug13 on the ceramic substrate 11 and the step of forming an interlevelinsulating film 15 on the entire surface of the resultant structure andforming a connection hole facing the interconnection 14.

As described above, according to this embodiment, the excess portion ofthe conductive paste 13 is removed in the step of temporarily hardeningthe paste, in which the paste can be easily removed, instead of the stepafter calcination in which the paste is difficult to remove. For thisreason, even if the trench 12 having a large opening diameter is formedto decrease the resistance of the chip-through plug, the excess portionof the conductive paste 13 can be removed in a short period of time.

In addition, in this embodiment, since the conductive paste 13 is buriedin the trench 12 after calcination of the ceramic substrate 11 (afterhigh-temperature heat treatment), a metal paste having a relatively lowresistance, e.g., Ni or Al, which has a melting point lower than that ofa refractory metal such as W can be used.

Furthermore, if the thick ceramic substrate 11 is used, since thesubstrate can be easily treated, the process required for the formationof the chip-through plug 13 is facilitated.

Although the excess portion of the conductive paste 13 is removed bypolishing in this embodiment, this portion may be removed by etchingsuch as RIE or CDE.

Note that the excess portion of the conductive paste 13 can be reliablyremoved by CMP regardless of the amount of the excess portion of theconductive paste 13 and its planarization before polishing. Thechip-through plug 13 having a flat upper portion can therefore be easilyformed. If the upper portion is flat, the interconnection 14 can beeasily formed on it.

(Sixth Embodiment)

FIGS. 7A to 7G are sectional views showing the steps in a method offorming a chip-through plug according to the sixth embodiment of thepresent invention. In this embodiment, a chip-through plug is formed inan Si substrate (Si wafer).

As shown in FIG. 7A, an interlevel insulating film 22 is formed on an Sisubstrate 21 on which a device has already been formed.

As shown in FIG. 7B, the interlevel insulating film 22 and the Sisubstrate 21 are etched to form a trench 23 having an opening diameterof 50 μm and a depth of 200 μm.

As shown in FIG. 7C, after a 1-μm thick silicon nitride film 24 isformed on the entire surface of the trench 23 to cover it by a plasmaCVD method, a multilayer metal film 25 made up of a 50-nm thick Ti film,a 300-nm thick Ni film, a 50-nm thick Pd film, and a 4-μm thick Cu filmis formed on the silicon nitride film 24. In this case, the Ti, Ni, andPd films are formed by, for example, sputtering, whereas the Cu film isformed by, for example, a plating method.

As shown in FIG. 7D, the entire surface of the resultant structure isthen coated with a conductive or insulating paste 26, and the paste 26having a thickness larger than the depth of the trench 23 is buried inthe trench 23. Thereafter, a temporary hardening process is performed byvolatilizing the solvent of the paste 26. At this time, a large amountof excess portion of the paste 26 remains outside the trench 23. In thiscase, the conductive paste 26 having a thickness smaller than the depthof the trench 23 may be buried in the trench 23 as long as the trench 23can be entirely filled with the paste finally.

Note that since the aspect ratio of the trench 23 is high, a pasteburying method described in the seventh embodiment is preferably used toprevent any void from being left in the trench 23.

As shown in FIG. 7E, the excess portion of the paste 26 outside thetrench 23 is removed by CMP. In this case, since the paste 26 hasundergone only the temporary hardening process, the excess portion ofthe paste 26 outside the trench 23 can be easily removed by polishingwith a weak force enough to destroy the resin in the paste 26. As aconsequence, as in the fifth embodiment, the excess portion of the paste26 can be removed in a very short period of time as compared with theprior art.

In addition, the excess portion of the paste 26 can be easily andselectively removed by adding a solution of the same solvent as that ofthe binder contained in the paste 26 or a solvent solution having adissolving powder lower than that of the above solvent to the polishingliquid. Alternatively, instead of the solution, a weak acid or weakbasic solution that dissolves the binder in the paste 26 may be added.

In this step, a certain portion of the paste 26 is preferably leftoutside the trench 23 for the following reason. Since the paste 26shrinks in the next calcination step, if all the portion of the paste 26outside the trench 23 is removed, an unfilled portion is formed in theupper portion of the trench 23 after calcination. If, however, the paste26 does not shrink much, no problem arises even if all the portion ofthe paste 26 outside the trench 23 is removed.

After the portion of the multilayer metal film 25 outside the trench 23and the silicon nitride film are removed by CMP or the like, the paste26 is calcined. The calcined paste 26, the multilayer metal film 25, andthe silicon nitride film 24 constitute a chip-through plug 27.Subsequently, as shown in FIG. 7F, a multilevel interconnection 28 isformed on the Si substrate 21.

As shown in FIG. 7G, the lower surface of the Si substrate 21 ispolished by CMP or the like until the chip-through plug 27 appears,thereby completing the chip-through plug 27 extending through the Sisubstrate 21. In this embodiment, as shown in FIG. 7G, the multilayermetal film 25 is etched when the lower surface of the substrate ispolished. Even if, however, this process is performed such that themultilayer metal film 25 is left in the bottom portion of thechip-through plug 27, no problem arises. The subsequent steps are thesame as those for a general multichip module. For example, the step ofconnecting a plurality of Si substrates 21 to each other throughchip-through plugs 27 continues.

As described above, according to this embodiment, the excess portion ofthe paste 26 is removed in the step of temporarily hardening the paste,in which the paste can be easily removed, instead of the step aftercalcination in which the paste is difficult to remove. As in the firstembodiment, therefore, the low-resistance chip-through plug 27 can beformed without taking much time. In addition, this embodiment can bemodified in the same manner as the fifth embodiment. For example, theexcess portion of the paste 26 may be removed by etching instead ofpolishing.

(Seventh Embodiment)

FIGS. 8A to 8D are sectional views showing the steps in a method offorming a chip-through plug according to the seventh embodiment of thepresent invention.

As shown in FIG. 8A, a trench 32 of a high aspect ratio is formed in anSi or ceramic substrate 31. For example, the trench 32 has an openingdiameter of 100 μm and a depth of 150 μm.

As shown in FIG. 8B, the substrate 31 is coated with an Ni paste 33, andthe trench 32 is filled with the Ni paste 33 to some level from theopening surface of the trench 32. In this stage, a void (unfilledregion) is present on the bottom surface side of the trench 32.

When an Si substrate is used as the substrate 31, an insulating filmsuch as a silicon nitride film 24 for providing insulation for the Sisubstrate is formed in advance on the surface of the trench 32, as inthe sixth embodiment. In addition, as in the sixth embodiment, thesubstrate may be coated with an insulating paste through a conductivefilm such as a multilayer metal film 25 instead of the Ni paste 33.

As shown in FIG. 8C, the Ni paste 33 is pressurized with N₂ gas 34 of ahigh pressure, e.g., 2 kgf/cm² to fill the void in the trench 32 withthe Ni paste 33, thereby entirely filling the trench 32 with the Nipaste 33, as shown in FIG. 8D.

The subsequent steps are the same as those in the fifth and sixthembodiments. For example, a temporary hardening process is performed ata temperature of 100 to 150° C. to remove the portion of the Ni paste 33outside the trench 32. The Ni paste 33 is then calcined at a temperatureof 600° C. The lower surface of the substrate 31 is polished until thiscalcined Ni paste 33 appears, thereby completing a chip having the Nipaste 33 penetrating the Si substrate 33.

As described above, according to this embodiment, after the Ni paste 33is buried in the trench 32 to a certain extent, the void in the trench32 is filled with the Ni paste 33 by pressurizing the portion of the Nipaste 33 outside the trench 32. With this process, even if the depth(aspect ratio) of the trench 32 increases, the trench 32 can be easilyfilled with the Ni paste 33.

According to this embodiment, even if, therefore, the depth of thetrench 32 increases, the Ni paste 33 without any void can be formed.

In this embodiment, after the substrate is coated with the Ni paste 33,the Ni paste 33 is pressurized with a gas. However, this paste may bemechanically pressurized to fill the void in the trench 32 with the Nipaste 33. Alternatively, after the substrate is coated with the Ni paste33 under a reduced pressure, the pressure may be restored to atmosphericpressure, thereby filling the void in the trench 32 with the Ni paste33.

The present invention is not limited to the above embodiments. Forexample, in each embodiment described above, the paste according to thepresent invention is applied to a chip-through plug. However, this pastecan be applied to other members such as damascene interconnections.Various changes and modifications of the embodiments can be made withoutdeparting from the spirit and scope of the invention.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. A method of manufacturing a semiconductorsubstrate, comprising the steps of: forming a trench in a major surfaceof a substrate; forming a calcination type paste inside and outside thetrench, and burying said paste in the trench; temporarily hardening saidpaste; removing said paste outside the trench; and calcining said paste.2. A method according to claim 1, wherein said paste outside the trenchis remove by one of polishing and etching.
 3. A method according toclaim 1, wherein a connection plug made of said paste extending throughthe substrate is formed by removing an opposite surface of the substrateto the major until said paste appears after the step of calcining saidpaste.
 4. A method according to claim 1, wherein an interconnection isformed on said paste after the step of calcining said paste.
 5. A methodaccording to claim 1, wherein a conductive paste is used as said paste.6. A method according to claim 1, wherein said paste outside the trenchis removed by chemical mechanical polishing.
 7. A method according toclaim 1, wherein a connection plug made of said paste extending throughthe substrate is formed by removing an opposite surface of the substrateto the major by one of polishing and etching until said paste appearsafter the step of calcining said paste.
 8. A method according to claim1, wherein a connection plug made of said paste extending through thesubstrate is formed by removing an opposite surface of the substrate tothe major by chemical mechanical polishing until said paste appearsafter the step of calcining said paste.